The real reason MS doesn't get tablets is that it's a new product category, and MS pretty much always thinks in terms of how to extend who they are (Desktop) into any new market. XBox hardly counts; while it's a great product they did not have to define the market in any way, they moved in and made a solid product in a well defined market. With Kinect they really did something outrageously cool, but this isn't usual for them.
Apple, on the other hand, has shown the ability to look at niche markets and see the bigger picture, turning it mainstream. iPod, iPhone, iPad: all of these areas had existing companies with somewhat successful products, but definitely niche.
Sometimes MS reminds me of Xerox's lack of foresight with PARC.